Update LVGL to v9.1.0

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diff --git a/lib/lvgl/docs/porting/timer_handler.rst b/lib/lvgl/docs/porting/timer_handler.rst
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+.. _timer:
+
+=============
+Timer Handler
+=============
+
+To handle the tasks of LVGL you need to call :cpp:func:`lv_timer_handler`
+periodically in one of the following:
+
+- *while(1)* of *main()* function
+- timer interrupt periodically (lower priority than :cpp:func:`lv_tick_inc`)
+- an OS task periodically
+
+Example:
+
+.. code:: c
+
+   while(1) {
+     uint32_t time_till_next = lv_timer_handler();
+     my_delay_ms(time_till_next);
+   }
+
+If you want to use :cpp:func:`lv_timer_handler` in a super-loop, a helper
+function :cpp:func:`lv_timer_handler_run_in_period` is provided to simplify
+the porting:
+
+.. code:: c
+
+   while(1) {
+      ...
+      lv_timer_handler_run_in_period(5); /* run lv_timer_handler() every 5ms */
+      ...
+   }
+
+Or use the sleep time automatically calculated by LVGL:
+
+.. code:: c
+
+   while(1) {
+     ...
+     lv_timer_periodic_handler();
+     ...
+   }
+
+In an OS environment, you can use it together with the **delay** or
+**sleep** provided by OS to release CPU whenever possible:
+
+.. code:: c
+
+   while (1) {
+      uint32_t time_till_next = lv_timer_handler(); 
+      os_delay_ms(time_till_next); /* delay to avoid unnecessary polling */
+   }
+
+To learn more about timers visit the :ref:`timer`
+section.
+
+API
+***